Effect of imbalance between energy and nitrogen supplies on microbial protein synthesis and nitrogen metabolism in growing double-muscled Belgian Blue bulls

Six double-muscled Belgian Blue bulls (initial weight: 345 +/- 16 kg) with cannulas in the rumen and proximal duodenum were used in two juxtaposed 3 x 3 Latin squares to study the effect of a lack of synchronization between energy and N in the rumen on microbial protein synthesis and N metabolism by giving the same diet according to three different feeding patterns. The feed ingredients of the diet were separated into two groups supplying the same amount of fermentable OM (FOM), but characterized by different levels of ruminally degradable N (RDN). The first group primarily provided energy for the ruminal microbes (14.6 g of RDN/kg of FOM), and the second provided N (33.3 g of RDN/kg of FOM). These two groups were fed to the bulls simultaneously or alternately with the aim of creating three different time periods of imbalance (0, 12, or 24 h) between energy and N supplies in the rumen. The introduction of imbalance affected neither microbial-N flow at the duodenum (P = 0.65) nor efficiency of growth (P = 0.69), but decreased (P = 0.016) the NDF degradation in the rumen 12.2% for a 12-h period of imbalance. N retention was not affected by imbalance (P = 0.53) and reached 57.8, 58.5, and 54.7 g/d, respectively, for 0-, 12- and 24-h imbalance. It seems that the introduction of an imbalance of 12 or 24 h between energy and N supplies for the ruminal microbes by altering the feeding pattern of the same diet does not negatively influence microbial protein synthesis or N retention by the animal. Nitrogen recycling in the rumen plays a major role in regulating the amount ofruminally available N and allows for continuous synchronization of N- and energy-yielding substrates for the microorganisms in the rumen. Therefore, a lack of synchronization in the diet between the energy and N supplies for the ruminal microbes is not detrimental to their growth or for the animal as long as the nutrient supply is balanced on a 48-h basis. Thus, these dietary feeding patterns may be used under practical feeding conditions with minimal effect on the performance of ruminant animals.     

Effect of rumen-degradable protein balance deficit on voluntary intake, microbial protein synthesis, and nitrogen metabolism in growing double-muscled Belgian Blue bulls fed corn silage-based diet

Two trials were conducted to evaluate the effect of rumen-degradable protein balance (OEB) deficit on voluntary intake (trial 1), microbial protein synthesis, and N metabolism (trial 2) in growing double-muscled Belgian Blue bulls. In trial 1, six bulls (339 +/- 26 kg of initial BW) were used in a replicated 3 x 3 Latin square and received a diet of 60% corn silage and 40% concentrate with ad libitum intake (DM basis). Three concentrates were formulated by adding urea at the expense of barley to give similar dietary contents of intestinal digestible proteins, NE for fattening, and fermentable OM, but with different levels of OEB. Thus, 2 levels of OEB deficit (-23.7 and -9.2 g of OEB/kg of DM) were compared with a diet providing a slight OEB surplus (5.3 g of OEB/kg of DM). Voluntary DMI decreased linearly (P = 0.02) with decreasing rumen-degradable protein balance. This decrease in intake could explain the linear decrease in ADG observed when negative OEB diets were fed. In trial 2, six bulls (304 +/- 12 kg of initial BW) with cannulas in the rumen and proximal duodenum were used in a replicated 3 x 3 Latin square and fed diets similar to those used in trial 1 at an intake level of 85 g of DM/kg of BW(0.75). Diurnal variations of ruminal NH(3)-N and plasma urea-N concentrations were greatly influenced by the level of OEB in the diet. No differences in NDF and starch degradation in the rumen, microbial N flow at the duodenum, or efficiency of microbial protein synthesis in the rumen were noted among the levels of OEB in diets. The reductions of the OEB value from 5.3 g/kg of DM to -9.2 g/ kg of DM and -23.7 g/kg of DM were associated with reductions of 26.5 and 48.8% in urinary N output. Absolute amounts of N retained by the bulls increased significantly with the level of OEB in diets. Indeed, 51.4% of the incremental supply of N was excreted between -23.7 and -9.2 g of OEB/kg of DM diets, and 74.6% of the incremental supply of N was excreted between -9.2 and 5.3 g of OEB/kg of DM diets. Feeding diets characterized by an adequate intestinal digestible protein supply and a OEB close to -10 g of OEB/kg of DM could be a feeding strategy to reduce N losses from the farm with little effect on the animal performance and voluntary intake. Reduced OEB may reduce N excretion in the environment but may also result in decreased N retention.     

Effects of dietary energy level and protein source on nutrient digestion and ruminal nitrogen metabolism in steers.

Four Simmental steers with ruminal, duodenal, and ileal cannulas were used to examine effects of dietary forage: concentrate ratio and supply of ruminally degradable true protein on site of nutrient digestion and net ruminal microbial protein synthesis. Steers (345 kg) were fed ammoniated corn cob (high forage; HF)- or corn cob/ground corn/cornstarch (low forage; LF)-based diets supplemented with soybean meal (SBM) or a combination of corn gluten meal and blood meal (CB). Diets were fed at 2-h intervals with average DM intake equal to 2.2% of BW. Feeding LF vs HF increased (P less than .05) OM digestion (percentage of intake) in the stomach, small intestine, and total tract. Efficiency of microbial CP synthesis (EMCP; g of N/kg of OM truly fermented) decreased (P less than .05) for LF vs HF (24.1 vs 26.8), but microbial N and total N flows to the small intestine were similar (P greater than .05) between energy levels (average 112 and 209 g/d, respectively). Total N flows to the small intestine were 13.1% greater (P less than .05) for CB than for SBM because of increased (P less than .05) passage of nonmicrobial N. Feeding SBM vs CB increased (P less than .05) EMCP (27.3 vs 23.3) and microbial N flow to the small intestine (127.5 vs 112.5 g/d), but these increases were not likely due to increased ruminal concentrations of ammonia N (NH3 N). Decreased (P less than .05) incorporation of NH3 N into bacterial N and slower turnover rates of ruminal NH3 N for SBM vs CB suggest that direct incorporation of preformed diet components into cell mass increased when SBM was fed. Results of this study suggest that the inclusion of ruminally degradable protein in the diet may increase the supply of products from proteolysis and that this can increase EMCP and microbial protein flow to the small intestine.     

Ruminal dynamics of ad libitum feeding in buffalo bulls receiving different level of rumen degradable protein

Four ruminally cannulated Nili-Ravi buffalo bulls were used in a 4 × 4 Latin Square Design to determine the influence of varying level of ruminally degradable protein (RDP) on dry matter intake (DMI), ruminal characteristics, digestibility, blood pH, blood urea nitrogen (BUN) and nitrogen (N) balance. Four isonitrogenous and isocaloric diets were formulated. The C diet contained 50% RDP while medium, high and very high RDP diets had 66, 82 and 100% RDP of the total crude protein (CP) and were denoted as MRDP, HRDP and VHRDP, respectively. The bulls were fed ad libitum. Nutrients intake decreased linearly with increasing the RDP proportion of total dietary CP. A quadratic effect of RDP on ruminal pH was noticed with increasing level of RDP with quadratic maxima at 66% RDP diet. Increasing level of dietary RDP also had a quadratic effect on total bacterial and protozoal count with maximum microbial count at 82% RDP diet. Increasing dietary RDP resulted in linear increase in DM digestibility. However, neutral detergent fiber digestibility was decreased linearly with increasing the level of dietary RDP. A linear increase in ruminal NH₃–N and BUN was noticed due to increasing level of dietary RDP. Higher positive N balance was noticed in bulls fed C diet compared to those fed MRDP, HRDP and VHRDP diets. The findings of this study indicated that buffalo bulls can effectively utilize 13.12% RDP of DM without any adverse effect on rumen and blood parameters.     

不同能氮同步化释放日粮对奶牛瘤胃体外发酵和微生物蛋白合成的影响

试验以3头安装永久性瘤胃瘘管的荷斯坦奶牛为试验动物,试验设计以不同RDN(g)/FOM(kg)比值日粮为底物,利用人工瘤胃体外培养法,通过瘤胃液pH值、瘤胃液氨氮浓度、挥发性脂肪酸含量、微生物蛋白含量这四个指标的测定,评价日粮RDN(g)/FOM(kg)比值分别为20、25、30、35的4种不同能氮同步化释放日粮对瘤胃发酵及微生物蛋白含量的影响。结果表明:随着体外培养时间的延长,瘤胃液pH值不断降低,pH均值以RDN(g)/FOM(kg)=25组为最高,RDN(g)/FOM(kg)=30组最低,差异不显著(P0.05)。NH3-N浓度随着RDN(g)/FOM(kg)水平的增加而增加,当RDN(g)/FOM(kg)=35时,NH3-N浓度均值最高。当RDN(g)/FOM(kg)=20时,细菌蛋白含量和原虫蛋白含量均最高。对于VFA当RDN(g)/FOM(kg)=30时,乙酸含量最高;当RDN(g)/FOM(kg)比值为20时,丙酸含量、丁酸含量最高;TVFA含量以RDN(g)/FOM(kg)=30时最高,乙酸、丙酸比值以RDN(g)/FOM(kg)比值为25时最高。     

不同蛋白质和碳水化合物饲料来源对牛瘤胃洗涤纤维降解和瘤胃液产物的定量研究

试验采用3×3拉丁方设计,3头安装永久性大口径瘤胃瘘管的青年母牛饲喂3种不同精饲料的日粮,3种精饲料分别为豆粕+玉米(日粮1),猪血粉+玉米(日粮2)和豆粕+小麦(日粮3)。精料日喂量按活牛体重的1%喂给,干玉米秸等量组成的日粮配给。试验为3个试验周期,每一周期为37d,其中适应期26d,在早晨采食后2、4、8、16和24h,分别5次实施瘤胃掏空,全量测定瘤胃物存留量。结果表明:日粮1在采食后2～8h瘤胃干物质、液体和NDF的存留量最低,与其他两种日粮相比差异显著(P<0.05);日粮1和日粮3瘤胃液氨氮存留量在采食后2～8h始终高于日粮2(P<0.05),但日粮3在采食4h后瘤胃液氨氮开始下降,而日粮1至采食后16h开始下降,日粮1瘤胃液氨氮数量采食后2～8h处于高峰状态,说明瘤胃微生物在瘤胃环境长时间一直保持稳定的降解能力;日粮1和日粮3在采食2～4h后处于较高的总挥发性脂肪酸(VFA)瘤胃存留量,日粮1在采食后8～16h瘤胃存留量降低,与日粮2和日粮3相比差异显著(P<0.05),日粮1对瘤胃VFA的快速移除,意味着瘤胃液的快速流出以及可能解释瘤胃固体物的快速移除。因此,日粮1和日粮3在牛瘤胃洗涤纤维降解和瘤胃液产物代谢模式发挥不同作用。     

日粮精粗比对瘤胃微生物合成效率的影响

本文用瘤胃持续模拟装置研究了精粗比为７：３、１：１和３：７时对日粮有机物、中洗纤维和酸洗纤维的降解、蛋白质的转化和微生物合成效率的影响。结果表明，精粗比不影响瘤胃微生物对可发酵能的利用效率（Ｐ〉０．０５），但是显著影响瘤胃微生物对可降解氮的利用效率（Ｐ〈０．０５）；最后探讨了瘤胃内可降解氮和可发酵能与微生物氮合成量之间的定量模型。     

Influence of direct-fed fibrolytic enzymes on diet digestibility and ruminal activity in sheep fed a grass hay-based diet

Six rumen-fistulated Merino sheep were used in a crossover design experiment to evaluate the effects of an exogenous fibrolytic enzyme preparation (12 g/d; ENZ), delivered directly into the rumen, on diet digestibility, ruminal fermentation, and microbial protein synthesis. The enzyme contained endoglucanase and xylanase activities. Sheep were fed a mixed grass hay:concentrate (70:30; DM basis) diet at a daily rate of 46.1 g/kg of BW(0.75). Samples of grass hay were incubated in situ in the rumen of each sheep to measure DM and NDF degradation. The supplementation with ENZ did not affect diet digestibility (P = 0.30 to 0.66), urinary excretion of purine derivatives (P = 0.34), ruminal pH (P = 0.46), or concentrations of NH(3)-N (P = 0.69) and total VFA (P = 0.97). In contrast, molar proportion of propionate were greater (P = 0.001) and acetate:propionate ratio was lower (P < 0.001) in ENZ-supplemented sheep. In addition, ENZ supplementation tended to increase (P = 0.06) numbers of cellulolytic bacteria at 4 h after feeding. Both the ruminally insoluble potentially degradable fraction of grass hay DM and its fractional rate of degradation were increased (P = 0.002 and 0.05, respectively) by ENZ treatment. Supplementation with ENZ also increased (P = 0.01 to 0.02) effective and potential degradability of grass hay DM and NDF. Ruminal fluid endoglucanase and xylanase activities were greater (P < 0.001 and 0.03, respectively) in ENZ-supplemented sheep than in control animals. It was found that ENZ supplementation did not affect either exoglucanase (P = 0.12) or amylase (P = 0.83) activity. The results indicate that supplementing ENZ directly into the rumen increased the fibrolytic activity and stimulated the growth of cellulolytic bacteria without a prefeeding feed-enzyme interaction.     

Manipulation of nitrogen digestion by sheep using defaunation and various nitrogen supplementation regimens

Five ruminally, duodenally, and ileally cannulated sheep (average BW 62 kg) were fed 65% roughage: 35% concentrate diets (CP = 15%) in a 5 x 5 Latin square design to study the applicability of using a combination of defaunation with N supplements (soybean meal [SBM], corn gluten meal [CGM], blood meal [BM], urea, and casein) with different extents of ruminal degradation to manipulate microbial protein synthesis and amount of ruminal escape protein. Diets were fed twice daily (1,759 g DM/d). Defaunation was accomplished with 30-ml doses of alkanate 3SL3 (active ingredient: sodium lauryl diethoxy sulfate)/sheep daily for 3 d with 2 d of fasting. Treatment 1 (control) involved feeding faunated sheep a diet in which the supplemental N (45% of total dietary N) was 67% SBM N and 33% urea N. Treatment 2 involved feeding defaunated sheep the same diet as the control. Treatments 3, 4, and 5 involved feeding defaunated sheep diets in which the supplemental N source was either 67% CGM-BM (1:1 N ratio) N:33% urea N, or 33% CGM-BM N:67% urea N or 33% CGM-BM N:33% urea N:33% casein N, respectively. Compared with the faunated control, defaunation decreased (P less than .05) ruminal ammonia concentration (19 vs 26 mg/dl) and increased (P less than .05) CP flow to the duodenum (253 vs 214 g/d) due to a trend for increases in both bacterial (BCP) and nonbacterial (NBCP) CP flows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of level of feeding and ruminally undegraded protein on ruminal bacterial protein synthesis, escape of dietary protein, intestinal amino acid profile, and performance of dairy cows.

Six cannulated lactating cows were used in two replicated, concurrently run 3 x 3 Latin square experiment to study the interaction between level of feeding and diets differing in ruminally undegraded protein (RUP) on bacterial protein synthesis, ruminal escape of dietary protein, and flow of total and individual amino acids (AA) to the small intestine. Treatments consisted of three diets formulated to contain 69 g (HL), 53 g (HH), and 48 g (LL) of RUP per kilogram of DM, respectively. Measurements were made in early lactation, at high feeding level (19.3 kg DM/d), and repeated at late lactation (9.8 kg DM/d, low feeding level) with the same animals and diets. Decreasing feed intake increased (P < .05) the apparent digestibility of OM, NDF, and ADF in the rumen and the total tract, decreased (P < .05) ruminal liquid and particulate passage rate and total ruminal VFA concentration, and increased ruminal pH and ammonia concentration. Decreased level of intake reduced the (P < .05) efficiency of bacterial N synthesis (28.1 vs 23.7 g bacterial N/kg OM truly digested in the rumen) and decreased (P < .05) ruminal protein degradation rate measured with an in situ method. Duodenal flow of nonammonia nitrogen (NAN), and total AA were highest (P < .05) for the HL diet and lowest (P < .05) for the LL diet at the high feeding level. However, at the low feeding level, diet composition did not affect the amount of NAN or total AA passing to the small intestine. Diet HL increased the proportion of Met, His (P < .05), and Arg (P < .07) in the duodenal digesta at both feeding levels. When purines were used to calculate bacterial N synthesis, no differences between diets were detected. However, when diaminopimelic acid was used, highest bacterial N synthesis was detected for diet HH at the high feeding level. Diet HL supported the highest (P < .05) milk protein production at the high feeding level, and the highest (P < .05) milk protein content at the low feeding level. In conclusion, level of feeding and amount of RUP altered the amount and composition of AA presented to the cows.     

The effects of high levels of rumen degradable protein on rumen pH and histamine concentrations in dairy cows

An experiment was conducted to test the hypothesis that the supplementation of crude protein (CP) results in rumen acidosis and increased histamine concentrations in dairy cows. Six ruminally fistulated, non-pregnant dry cows were fed three experimental rations in a replicated 3 × 3 Latin square design. The CP contents in the low-CP, the high rumen undegradable protein (high-RUP) and the high rumen degradable protein (high-RDP) rations were 112, 259 and 266 g/kg dry matter (DM) respectively. The cows were fed 7.7 kg DM of the concentrates and 2.7 kg DM of rice straw. High levels of RDP in the ration significantly increased the ammonia, total volatile fatty acid (VFA) and histamine concentrations in the rumen fluid. However, supplemental CP, whether degradable or undegradable, did not significantly affect the pH of rumen fluid. Plasma urea nitrogen concentration was higher in both high-RDP and high-RUP in relation to cows fed the low-CP ration. The rise in ruminal histamine concentrations was physiologically non-relevant, most likely because rumen pH was not affected by supplemental CP at the installed level of DM intake. Therefore, it can be concluded that the issue of supplemental CP, rumen pH and ruminal histamine concentrations has not yet been settled. Further research is warranted to understand these relationships.     

Influence of varying levels of dietary cation anion difference on ruminal characteristics,nitrogen metabolism and in situ digestion kinetics in buffalo bulls

This study was conducted to examine the influence of varying dietary cation anion difference (DCAD) on nutrient intake, digestibility, ruminal characteristics, blood acid base status and in situ digestion kinetics in Nili Ravi buffalo bulls. Four iso‐nitrogenous and iso‐caloric diets having ?110, +110, +220 and +330 mEq/kg dry matter (DM) DCAD were formulated which were represented by A (anionic), LC (low cationic), MC (medium cationic) and HC (high cationic), respectively. These diets were used in four ruminally cannulated Nili Ravi buffalo bulls in a 4 × 4 Latin Square Design. Improved nutrient intake was recorded at high DCAD levels while digestibility remained unaffected. Ruminal ammonia nitrogen, rumen pH, acetate and acetate : propionate ratio were higher in buffalo bulls fed MC and HC diets than those fed A and LC diets. Blood pH and HCO₃^‐ also tended to increase as DCAD level was increased in the diet. Serum Ca and Cl concentrations were higher in bulls fed A and LC diets whereas serum Mg, P and S remained unaffected. Urine pH increased with increasing DCAD level. Nitrogen intake and blood urea nitrogen concentrations were also higher in bulls fed MC and HC diets. There was a consistent increase in ruminal DM and neutral detergent fiber degradability, rate of disappearance and extent of digestion at high DCAD levels in the diet. However, lag time decreased at high DCAD level. This study indicated that buffalo bulls fed MC and HC diets improved feed intake, ruminal characteristics and digestion kinetics.     

Accounting for the effects of a ruminal nitrogen deficiency within the structure of the Cornell Net Carbohydrate and Protein System

The Cornell Net Carbohydrate and Protein System (CNCPS) prediction of fiber digestion and microbial mass production from ruminally degraded carbohydrate has been adjusted to accommodate a ruminal N deficiency. The steps for the adjustment are as follows: 1) the ruminal available peptide and ammonia pools are used to determine the N allowable microbial growth; 2) this value is subtracted from the energy allowable microbial growth to obtain the reduction in microbial mass; 3) this mass reduction is allocated between pools of bacteria digesting fiber (FC) and nonfiber (NFC) carbohydrate according to their original proportions in the energy allowable microbial growth; 4) the reduction in fermented FC is computed as the FC bacterial mass reduction divided by its yield (g bacteria/g FC digested); and 5) this reduction is added to the FC fraction escaping the rumen. Five published studies included information that allowed us to evaluate the response of animals to added dietary N. These evaluations compared observed and CNCPS-predicted ADG with and without this adjustment. The adjustment decreased the CNCPS overprediction of ADG from 19.2 to 4.7%, mean bias declined from .16 to .04 kg/d, and the r2 of the regression between observed and metabolizable energy (ME) or metabolizable protein allowable ADG was increased from .83 to .88 with the adjustment. When the observed dry matter intake was regressed against CNCPS-predicted DMI with an adjustment for reduction in cell wall digestibility, the r2 was increased from .77 to .88. These results indicated the adjustment for ruminal nitrogen deficiency increased the accuracy of the CNCPS model in evaluating diets of growing animals when ruminally degraded N is deficient.     

Influence of protein type and level on nitrogen and forage use in cows consuming low-quality forage

Minimal quantities of ruminally degradable protein from supplements may improve supplement use efficiency of ruminants grazing dormant forages. In Exp. 1, N retention, ruminal NH(3), serum urea N, and NDF digestibility were evaluated for 12 ruminally cannulated cows (Bos spp.) in an incomplete Latin Square design with 3 periods of 42 d each. Cows were fed weeping lovegrass [Eragrostis curvula (Schrad.) Nees] hay (4.1% CP, 75% NDF, OM basis) at 1.3 % BW/d and offered 1 of 3 sources of CP [urea, cottonseed (Gossypium spp.) meal (CSM); or 50% blood meal and 50% feather meal combination (BFM)] fed to supply 0, 40, 80, or 160 g/d of CP. Beginning on d 22 of supplementation, ruminal contents and serum samples were collected at -2, 0, 3, 6, 9, 12, 18, 24, 30, 36, and 48 h relative to the morning offering of hay. On Day 24, feces and urine were collected for 72 h. In Exp. 2, 4 ruminally cannulated steers were used in a replicated 4 by 4 Latin Square to evaluate use of supplements differing in quantity and ruminal CP degradability. Steers were fed 6.8 kg/d chopped sudangrass [Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex Davidse] hay (3.7% CP, 74% NDF on OM basis) and supplemented with 56 g/d of a salt mineral mix (CON); CON + 28 g/d blood meal + 28 g/d feather meal (BFM); CON + 98 g/d CSM (LCS); or CON + 392 g/d CSM (HCS). Treatments provided 0, 40, 40, or 160 g/d of CP for CON, BFM, LCS, and HCS respectively. In Exp. 1, N use and total tract NDF digestibility were not affected by protein sources or amounts (P ≥ 0.18). Ruminal NH(3) concentrations exhibited a quadratic response over time for UREA (P < 0.05) and was greater with increasing inclusion of urea (P < 0.05); whereas BFM or CSM did not differ (P > 0.05) by amount or across time. In Exp. 2, supplementation had a tendency (P = 0.09) to increase DM disappearance. Supplementation also increased (P < 0.01) serum glucose concentrations; however, no difference (P ≥ 0.28) was found between supplements. Serum urea N and ruminal NH(3) concentrations were increased (P ≤ 0.01) in steers fed HCS. Feeding low quantities of a high-RUP supplement maintained rumen function without negatively affecting DM or NDF digestibility of a low-quality forage diet.     

Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows

The objectives of this experiment were to investigate the effects of two ruminally degradable protein (RDP) levels in diets containing similar ruminally undegradable protein (RUP) and metabolizable protein (MP) concentrations on ruminal fermentation, digestibility, and transfer of ruminal ammonia N into milk protein in dairy cows. Four ruminally and duodenally cannulated Holstein cows were allocated to two dietary treatments in a crossover design. The diets (adequate RDP [ARDP] and high RDP [HRDP]), had similar concentrations of RUP and MP, but differed in CP/RDP content. Ruminal ammonia was labeled with 15N and secretion of tracer in milk protein was determined for a period of 120 h. Ammonia concentration in the rumen tended to be greater (P = 0.06) with HRDP than with ARDP. Microbial N flow to the duodenum, ruminal digestibility of dietary nutrients, DMI, milk yield, fat content, and protein content and yield were not statistically different between diets. There was a tendency (P = 0.07) for increased urinary N excretion, and blood plasma and milk urea N concentrations were greater (P = 0.002 and P = 0.01, respectively) with HRDP compared with ARDP. Milk N efficiency was decreased (P = 0.01) by the HRDP diet. The cumulative secretion of ammonia 15N into milk protein, as a proportion of 15N dosed intraruminally, was greater (P = 0.003) with ARDP than with HRDP. The proportions of bacterial protein originating from ammonia N and milk protein originating from bacterial or ammonia N averaged 43, 61, and 26% and were not affected by diet. This experiment indicated that excess RDP in the diet of lactating dairy cows could not be efficiently utilized for microbial protein synthesis and was largely lost through urinary N excretion. At a similar MP supply, increased CP or RDP concentration of the diet would result in decreased efficiency of conversion of dietary N into milk protein and less efficient use of ruminal ammonia N for milk protein syntheses.     

红豆草缩合单宁对绵羊瘤胃代谢及饲粮尼龙袋降解率的影响

选用3只1岁半、平均体重24 kg,安装永久瘤胃瘘管的甘肃高山细毛羊羯羊,按3×3拉丁方试验设计,每个循环19 d(预试期10 d,正试期9 d),研究饲粮中红豆草缩合单宁水平对绵羊瘤胃代谢的影响。试验共设3个处理饲粮,其中红豆草缩合单宁水平依次是Ⅰ为0.00 g/kg DM、Ⅱ为1.52 g/kg DM、Ⅲ为3.03 g/kg DM。试验结果表明,3个处理的瘤胃液pH均值(依组次为6.24±0.32,6.13±0.28和6.13±0.37)无显著差异(P＞0.05);处理Ⅱ、Ⅲ瘤胃液总挥发性脂肪酸(TVFA)呈高于Ⅰ的趋势(P=0.099);处理Ⅲ的乙酸摩尔比低于处理Ⅰ(P＜0.05)与Ⅱ(P=0.074),其丙酸摩尔比较高(P=0.088),乙酸/丙酸较低(P=0.096);各处理间瘤胃液总氮、蛋白氮、细菌氮、氨态氮、尿素氮的平均浓度差异均不显著(P＞0.05)。因此,本试验结果表明,含红豆草缩合单宁3.03 g/kg DM的饲粮对绵羊瘤胃纤维素分解微生物的活性产生一定程度的抑制,而分解淀粉的微生物活性被增强。     

Comparative investigation of salinomycin and flavophospholipol in sheep fed different composed diets.

The effects of salinomycin and flavophospholipol, and their relationship with the diet, were studied in nine ruminally and duodenally cannulated wethers. Within the composition of the ration, the levels of rumen degradable protein (RDP) and non-structural carbohydrates (NSC) were changed (diet H: 74% RDP and 38% NSC; diet M: 57% RDP and 32% NSC; diet L: 48% RDP and 23% NSC). There was no clear treatment effect of flavophospholipol on propionate concentration. Salinomycin supplementation appeared to be more effective than flavophospholipol in the increase of propionate concentration at the expense of acetic acid. Salinomycin significantly reduced the ammonia concentration of the rumen fluid. Microbial N content of the duodenal digesta was significantly lower when salinomycin was used. Salinomycin inhibited proteolysis and reduced the efficiency of microbial protein synthesis. The effect of salinomycin on ruminal N metabolism was independent of the composition of substrate. Unlike salinomycin, flavophospholipol tended to increase proteolysis in the rumen and did not inhibit protein synthesis. The effect of salinomycin on ruminal fermentation and the duodenal flow of nutrients were independent of substrate composition.     

Effects of sodium selenite addition on ruminal fermentation,microflora and urinary excretion of purine derivatives in Holstein dairy bulls

Researches on sodium selenite (SS) mainly focus on production performance and rumen fermentation in ruminants, and the influence of dietary Se addition on ruminal microbial population and enzyme activity in dairy bulls is scarce. This study mainly evaluated the effects of SS on ruminal fermentation, microflora and urinary excretion of purine derivatives (PD) in dairy bulls. Eight ruminally cannulated dairy bulls were used in a replicated 4 × 4 Latin square design. Treatments were control, low SS (LSS), medium SS (MSS) and high SS (HSS) with 0, 0.1, 0.3 and 0.5 mg/kg of selenium (Se) from SS in dietary dry matter (DM), respectively. The supplement of SS (1.0 g/kg of Se) was mixed into the first third of the daily ration. Bulls were fed a total mixed ration with corn silage to concentrate ratio of 50:50 on a DM basis. Dry matter intake was not affected, average daily gain linearly increased, while feed conversion ratio quadratically decreased with increasing Se addition. The linearly increased digestibility of DM, organic matter, crude protein, ether extract, neutral detergent fibre and acid detergent fibre was observed. Both ruminal pH and ammonia‐N concentration linearly decreased, whereas total volatile fatty acid concentration linearly increased. A lower acetate to propionate ratio was observed due to the unchanged acetate proportion and increased propionate proportion. Activity of cellobiase, xylanase, pectinase, α‐amylase and protease, populations of total bacteria, fungi, protozoa, Ruminococcus (R.) albus, R. flavefaciens, Fibrobacter succinogenes, Butyrivibrio fibrisolvens and Ruminobacter amylophilus as well as urinary total PD excretion linearly increased, whereas populations of total methanogens and Prevotella ruminicola linearly decreased. The data indicated that dietary Se addition stimulated ruminal microbial growth and enzyme activity, and resulting in the increased nutrient digestion and growth performance, and the optimum supplementary dose of Se was 0.3 mg/kg dietary DM from SS in dairy bulls.     

Effects of protozoa on bacterial nitrogen recycling in the rumen

The effects of protozoa on ruminal NH3-N kinetics and bacterial N recycling were measured in five sheep (57.6+/-7.1 kg BW, x +/- SD) with ruminal and duodenal cannulas in naturally faunated, defaunated, and refaunated periods. The sheep were fed a diet of 239 g of alfalfa haylage and 814 g of barley concentrate per day (DM basis) divided into 12 equal portions and allocated at 2-h intervals. A pulse dose of 300 mg of 15N as [15N]NH4Cl was administered into the rumen (on d 1 and 15) and 300 mg of 15N as [15N]urea was administered intravenously to the blood (d 8). Enrichment of 15N was measured in ruminal NH3-N, bacterial N, and plasma urea N over a period of 35 h. Total collection of urine was made for 5 d and analyzed for purine derivatives to calculate the flow of microbial N. Ruminal parameters and nutrient digestibilities were also measured. Sheep were defaunated using a rumen washing procedure 50 d prior to measurements in the defaunated period. Sheep were refaunated with ruminal contents from a faunated sheep receiving the same diet. Measurements began 26 d following refaunation, at which time protozoal numbers had returned to those in the originally faunated sheep. Data reported in parentheses are for faunated, defaunated, and refaunated sheep, respectively. Total culturable and cellulolytic bacterial numbers were unaffected by defaunation, but there was an increase in flow of microbial N from the rumen (10.8, 17.3, and 11.1 g N/d; P < .05) in the defaunated period. Flux, irreversible loss, and intraruminal recycling of NH3-N and recycling of NH3-N from plasma urea N were not affected by defaunation. Defaunation had no effect on reducing the absolute amount (13.8, 10.0, and 11.3 g N/d; P > .20) of bacterial N recycling and the percentage of N flux through the bacterial N pool. Total-tract digestion was reduced in defaunated compared with faunated sheep by 8, 17, 15, and 32% for OM, N, NDF, and ADF, respectively. In conclusion, defaunation improved ruminal N metabolism through the enhancement of bacterial protein synthesis, and improvement in the flow of microbial protein to the host animal.     

低淀粉饲粮条件下不同瘤胃降解淀粉水平对体外瘤胃发酵的影响

本试验旨在研究玉米作为淀粉来源的低淀粉饲粮条件下不同瘤胃降解淀粉(RDS)水平对体外瘤胃发酵的影响。以3头安装有永久性瘤胃瘘管的健康荷斯坦奶牛作为瘤胃液供体,各组分别以不同RDS水平饲粮作为发酵底物,体外产气法测定培养48 h时产气量和瘤胃发酵参数以及24 h时瘤胃微生物区系变化。结果表明:1)随着饲粮RDS水平的提高,体外培养48 h时产气量、潜在产气部分和产气速率呈线性升高(P0.05),快速发酵部分产气量呈线性下降(P0.05),干物质消失率呈线性升高(P0.05);2)随着饲粮RDS水平的提高,体外培养48 h时发酵液微生物蛋白、乙酸、丙酸、丁酸和总挥发性脂肪酸浓度呈线性升高(P0.05),pH和氨态氮浓度没有显著变化(P0.05);3)随着饲粮RDS水平的提高,体外培养24 h时发酵液中白色瘤胃球菌和嗜淀粉瘤胃杆菌的相对数量呈线性升高(P0.05),黄色瘤胃球菌、琥珀酸丝状杆菌、溶纤维丁酸弧菌、牛链球菌和溶淀粉琥珀酸单胞菌的相对数量没有显著变化(P0.05)。综合考虑,低淀粉饲粮条件下提高RDS水平有利于瘤胃发酵。